Tunnel digging machines or tunnel boring machines are known, which comprise a movable structure having large dimensions which is called a shield, having a substantially circular cross-section the diameter of which corresponds to the diameter of the tunnel the digging of which is made.
A roller cutter, or cutting disk, is a cutting tool freely revolving around a shaft attached to the cutting head of a tunnel boring machine. During rotation of the head and under the influence of thrust, the roller cutter rolls over the cutting face and chips out the rock in the form of scale-like plates.
Thus, the cutting head includes a plurality of roller cutters evenly distributed over its surface.
Conventionally, the roller cutters are mounted within a cutter holder on the cutting head by means of bolts. For this, the cutter holder comprises a housing, adapted to be attached to the tunnel boring machine shield and defining a chamber arranged to accommodate the roller cutter. Tightening supports are attached on or formed with outer faces of the roller cutter and comprise two blocking surfaces adapted to engage with a manual locking system. This locking system comprises in particular wedges, adapted to engage between cavities of the housing and blocking surfaces of the tightening supports. These wedges are attached in position in the cavities using several screws, bolts, etc. in order to prevent the roller cutters from being moved out from the housing, in spite of the harsh operating environment of the roller cutter.
The problem of changing the roller cutters occurs particularly in the case of a confined face tunnel boring machine, because access to the cutting head and to the roller cutter attachments (wedges, screws, etc.) is difficult and the working environment is under hyperbaric conditions. In such tunnel boring machines, the changing of the roller cutter is carried out, for safety reasons, from the rear of the cutting head, that is the side of the cutting head opposite the cutting face.
The procedure for changing a roller cutter often demands the exertion of considerable forces for loosening the used roller cutter from its housing, due to jams and the absence of guidance for the roller cutter, which is poorly compatible with work under hyperbaric conditions.
At present, the procedure for changing a roller cutter consists in equipping the roller cutter with lifting eyes, lifting it using a pulley block running along a rail, to load it onto a cart running through the equipment airlocking and bringing it back to the rear inside the shield, at atmospheric pressure. During dismantling, it is also necessary to progressively collect all the elements (wedges, screws, bolts, etc.) necessary for mounting the roller cutter and which will be used for mounting the new roller cutter.
Before inserting the new roller cutter in its housing, it must be properly positioned, which requires a painstaking manual intervention. Once the roller cutter is pushed towards its operating position, several blocking wedges are then put in place. Documents JP H10 140980, JP 2007/070825, JP H07 180488 and FR 2 758 853, could in particular be referred to, which describe cutting tools comprising roller cutters attached in a housing on the cutting head using wedges held fixed in position with respect to the housing by means of bolts, screws and/or journals.
It will be understood therefore that this procedure is long and tedious for the operators.
Thus, it has been provided in document WO 2011/076616 on behalf of the applicant, a new roller cutter comprising a locking member adapted to be immobilized in the housing, such that the roller cutter makes up a rigid block in view of the handling thereof, and means for prestressing the roller cutter that can include integrally borne screws of the roller cutter. In a particular embodiment, the locking member includes a bayonet adapted to cooperate with a cavity of the housing and rotatably movable between a position of inserting the roller cutter in the housing and a position of locking the roller cutter in the housing.
However, in use, the roller cutter undergoes very high pressure and vibration stresses which might move out the bayonet. Indeed, it is difficult to apply a prestressed strain enough to resist the vibrations of the roller cutter in a hard field.